The road to the Grand Canyon from the south crosses a gently rising plateau that gives no hint at what is about to unfold. You wonder if you have made a wrong turn. All at once an immense gorge a mile deep and up to 29 kilometres wide opens up. The scale is so vast that even from the best vantage point only a fraction of the canyon's 446 kilometres can be seen.

Nearly five million people travel here each year; 90 percent first see the canyon from the South Rim with its dramatic views into the deep inner gorge of the Colorado River. So many feet have stepped cautiously to the edge of major overlooks that in places the rock has been polished smooth. But most of the park's 1,904 square miles are maintained as wilderness. You can avoid crowds by hiking the park's many trails or driving to the cool evergreen forests of the North Rim where people are fewer and viewing is more leisurely. The Grand Canyon boasts some of the nation's cleanest air, with visibility on clear days averaging 145 to 175 kilometres.

It's hard to look at the canyon and not be curious about geology. Rock that dates back 1.8 billion years lies at the bottom. Exactly how the river formed the canyon is still unclear, but geologists generally agree that most of the cutting occurred within the last five million years.